Fatty acid recovery from soap stock



March 10, 1959 Alexa/Ae T. H. KELLEY 2,877,249

FATTY ACID RECOVERY FROM SOAP STOCK Filed Feb. 8, 1954 ral/r11 Wafer a//d frye /Yeldae 1N VENT'OR MM/ Af. )(11% l BY MEN, 0.a/ Mwah ATTORNEYS fusable quali It.is an object ofthisinventionvto provide an improved process for recovering fatty acids Lfrom soap is'increased. j- A' Still'another object is to provide a process for recovering fatty acids from soap' stock which substantially decreases the amount of color-producing impurities solubilized in the acidulated soap stock.

7 'Still :another object is to provide a process for' recoverin'g vfatty acids from soap stock'which affords a' sub- 4stantial economic; advantage over those processes now.

asn/,249 I 'FATrY Aon) REcovERYIgRoM soar. s'rocx Thomas Hardy Kelley, Ohioyasslguor, by:

mesne assignments, to The Buckeye Cellulose Corporation, Cincinnati, Ohio, acorppration of'Ohio Application Februar-y 3;1954', serial No. `401;,'163

6 claims] (c-L'zsous'y This invention relates to a process" for i' recovering fatty acids from soap stock obtained'from the caustic refining f Vegetable oils. Y a

2,877,249 Patented Mari rb ,AICC

' solvent v"phase which contains fatty acids and neutral oil in solution and removing the solvent from the fatty material.

This process may be applied in the treatment of soap stock derived from vegetable oils generally and those of the oleic-linoleic acid group, e. g. cottonseed, peanut,

corn, sesame, and the linolenic acid group, e. g. linseed,

soybean, hempseed, in particular. (Classifications, for

Industrial Oil and Fat Products by A. E. Bailey, 1951.

pp. 12o-124.)

In a preferred method of praticingthisvinvention, soap stock obtained from' the caustic refining of cottonseed oil 4is first mixed with water and hexane.

mixture of soap stock, water and hexane is then adjusted 15' to a value in the range from about 3.0 to 8.5 by the In the generally practiced method yofreiining vege-4 table oils, the crude oil isf treated with suicient-caustic soda solution to neutralizejthegfree fatty acids present with the formation of 'soap and to' react withl gums,

color imparting bodies and other impurities alsofpresent..

in the oil. In the process, the soap," precipitated impurities and emulsiiied excess caustiesola solution containing some dissolved impurities, arecoagulated by -proper temperature control. to facilitate separation from thejreiined oi1,and,bec ause ofthe emulsifying power of the combination, an appreciable amount of neutral oil v becomes emulsiiied withfthe soap, excess lye andy impurities. This combination of soap, excess lye, impurities and emulsilied oil is referred to generally in the industry as soap stock or foots.

The soap stock formed-in this way is separated from .the main body of the, refined oil either by gravity or Acentrifugally and maybe sold for soap manufacture. Normally, however, it is vacidulated torecover lthe fatty material present.- This `acidulationis usually accomplished in the industry in a batch type operation by The acidulated soap stock of v ery poor quality. The neutral oil contained in the soap stock is also present `infthisacidulated soap stock and it is normally further treated, as by twitchellizing.l

or..hydro1yzing,v to convert this neutral oil tofatty acid.

'Following this treatment, the hydrolyzedor twitchellzed mixture is usually distilled to obtain. fatty acids of a stock.

' Another object is to provide a continuous process for yrecovering fatty acids from soap stock.

Another object is to `provide a process for vrecovering fatty acids from soap stock by acidulation whereby the total vfatty acid content ofv the acidulated soap stock in use in the industry.

I have found that these objects can -beaccomplished f'bymixing' the soap stock with'wa'ter' and a'substa'ntially water-insoluble solvent "for 'the vfatty components, adding -suflicient acid to -the mixture to bringfit'to apHjiu the 'range from about 3.0 to 8.5 at' a temperature belwits' boiling point, separating the aqueous phase from the of the hexane.

The pH of the addition of sulfuric acid while the mixture is ybeing agitated. This acidulation is carried out at a temperature below the boiling point of the mixture and preferably at from about room temperature (65 70 F.) to 135 F.

.The acidulated mixture is'then centrifuged at a tempera- `ture' `within this rangeto separate the fatty miscella (mixture of fatty acid, neutral oil and hexane) from the aqueous phase. The fatty acid-neutral oil mixture is then recovered from the separated miscella by distillation The aqueous phase is normally lheated or distilled to recover any residual solvent and is then usually discarded.

The amount of water added in the above process is not critical and I have found that amounts up to about three times the Weight of the soap stock being ltreated are entirely satisfactory. (In this regard, I should specifically like to point out that very often my process may be carried out without the addition of water, the amount of Water present in the soap stock beingsulicient to the satisfactory operation of the process.) Amounts of hexane from about one-half to three times the weight of the soap stock may be used.

Depending upon the particular application, following the removal of hexane, the fatty acid-neutral oil mixture may be used directly in the manufacture of soap or other products without further processing, orthemixture may lbe twitchellzed or hydrolyzed to convert the neutral oil to fatty acids, or distilled either before or after conversion of the neutral oil to fatty acids.

The drawing forming part of this application is a schematic diagram representing apparatus suitable for practicing my process in a continuous manner. In the process, refinery foots, hexane, water (if necessary) and sulfuric acid are continuously added to mixing'tank 1, which is provided with agitating means, the ramount of acid added being regulated so that the pH of the mixture is held at the desired level as hereinbefore described. The acidulated mixture from this tank is then'continuously passed to centrifuge 2 wherein the fatty miscella phase and the aqueous phase are separated. The separated fatty miscella phase passes continuously to evapo- A rator 3 wherein a portion of the hexane is vaporized from the miscella. This vaporized hexane is then passed through condenser 5 and recovered in liquid form. The separated aqueous phase goes'to evaporator 4 wherein any hexane remaining in this phase is vaporized and also passed to condenser 5. The fatty misce1la, partially free of hexane, is then put through stripping column a' wherein the remainder of the hexane in themiscella is removed, passing tocondenser 7. The hexane-free fatty acidscoming from the stripping column are normally sent to storage.

It is to be understood that the above description of suitable apparatus is not to be interpreted as limiting my process in any way and that the various operations, e. g., centrifuging, evaporation, condensing, may be satisgfactorily accomplished with a variety lof equipment available on the open market.

A'The acidulation procedure common to the industry, i. e., boiling of the soap stock after the addition of a large excess of acid 4causes a retention of the impurities. pres- 'ent inthe soap stock inthe acidulated soap .stock and, as'4 pointed out hereinbefore, results in acidulat'ed soap stock which may bel of veryV poor quality. `On the other hand, acdulation according to the. presentrinvention, i. e., in the presence of hexane, at a pH from about 3.0 to 8.5 and at a temperature below the boiling point of the. mixture, apparently decreases the tendency of the fatty miscella to retain the impurities and instead leaves able impurities initially presentin the soap stock.

" The optimum separation of the fatty acid miscellal and kv'the' aqueous phase with my process occurs at a pH f in the range from about 5.0 toy 7.0 and when the con- "centration of fatty acids and neutral oil in hexane is "fromV about 5 to 15%. I normally prefer to carry out -the acidulation at a pH of about 5.0 to 5.5 and at from room temperature (65 F.) up to about 120"V F. Operation' under these conditions has the additional economic advantages of reducing corrosion of equipmentV to a negligible factor, decreasing very substantially the amount of mineral acid usedin the acidulation and eliminating water washing of the separated-fatty miscella to remove the mineral acid. Moreover, operation at the low temperatures results in aconsiderable saving in steam costs.

It is to be appreciated that my process may-becar- `ried out as either a batch operation or continuously. Also, solvents other than hexane, andgenerally, those solvents which are substantially insoluble in water and which are capable of dissolving fatty acids and oils, such as, for example, those having theV aforesaid characterstics'which are Vset forth in the article by A. Ernest Mac'Gee appearing in the August 1947 issue of the Oil Mill Gazetteer, may be used in the process with comparable results. Those solvents which are most generally used and which are preferred for use in the practice of the present invention are:

wacom-minous B.r Those of the halogenated hydrocarbon type, such as- VMethylene chloride Chloroform yCarbon tetrachloride Trichlorethylene Perchlorethylene Ethylene dichloride Tetrachlorethane C. Those ofthe petroleum Anaphtha type,.such.as-

" l. Iso-pentane 2. N-pentane 3. VN-hexane '4. 2-me'thyl pentane "these impurities in the aqueous phase. VConsequently, the acidulated soap stock produced according to the present process contains a muchlesser amount of -theundesir- S-methyl "pentane 2-3-dimethyl butane .'N-heptane 2-methy1hexane" S-methyl hexane 2-2-dimethyl pentane N-octane Z-methyl heptane 4-methyl heptane 4-methyl heptane 2-4-'dimethyl hexane 3-4-dimethy1'V hexane 2-5-dimethyl hexane 2-2-3-trimethyl pentane 2-2-4-'trimethyl pentane 2-2-33tetramethyl butane vN-,nonane .2-m'ethyl octane S-methyl octane 4-methyl. octane 2-4-dimethylheptane 2-2-5-trimethy1 hexane Decane Undecane Duodecane .'fTudecane AAgents e other* thanA sulfurio acid, sucht asl rnitriczaxtid,

hydrochloric acid,'vor=-acid' saltscapable of-redu`cing thel pH `to the desired 'range *areY equallyfeifective :for

acidulating theV 'soaprstock-solventmixtures Organic acids,lsuchas acetic,-mayV also be used'in'the acidulation but from an economic standpoint'are not-v asfdesirable fattymiscella in eachfcase was freed vof hexane by vacuum as the aforementioned agents.

The following examples' are-by way of illustration only-and the invention is'lnot--to be considered as limited i thereby but only by'the scope ofi-the appended claims.

Example` 1.-'-Soap ystock lfrom'the causticv refining of -cottonseed oil Was'mix'ed-with water andfhexane inthe distillation andthe totalv fatty acid content ofthe hexane- *free acidulated soap stock was determined according to f the :oflicial method G3-39 of the American Oil Chemists Society.

The blank-runewas made' under conditions `common .to the industry andcomprised acdulating" 'cottonseedg oil soap stock by boiling with alargeexcess of sulfuric acid followed by separation of the aqueous Aand fattyy acidneutral oil phases. Results on-"yield of total fatty'acids -`appear in theA table below.

`It maybeseen fromthe above-table that the-total vfatty acid content/of the' fatty` acid-neutral oil-phase separated from cottonseed oi1.-soap. fstock ris lsubstantially increased when the process of the presentA invention isernployed. f

- r.The hexaneffree vacidulatedsoap stocks abovewe're distilled to.. separate-the fatty acids. lColor-determina tions, according to .ocial methody Ce1f36-45l of the Amer-- .Y ican Oil v'Chemists-Society, werethen made on ythe freshly distilled fatty acids and after the distilled acids had aged overnight at about 180 F. with the following results.

Color (Red) Fresh Aged Ratio by Weight, Soap Stock: Added WaterzHexane Percent The TFA values in the above table may be compared with TFA values in the range from about 70 to 83 which are normal to acidulated soap stocks obtained by boiling this cottonseed oil soap stock with a large excess of acid.

Example 3.-Several samples of soap stock from the caustic refining of soybean oil were mixed with hexane and acidulated with sulfuric acid according to the process of the present invention and under the conditions indicated in the table below. The acidulated mixtures were centrifuged to separate the fatty miscella from the aqueous phase, the fatty miscella was freed of hexane by vacuum distillation and the total fatty acid content of the hexane-free acidulated soap stock was determined according to the aforementioned ofcial method of the American Oil Chemists Society. Results on yield of total fatty acids are included in the following table.

As pointed out hereinbefore, the process of my inventino may also be applied in the treatment of soap stock obtained from the refining of other vegetable oils and it is to be understood that other oils, solvents and acidulating agents in comparable proportions may be substituted in the aforesaid specific examples with comparable results.

Having thus described my invention, I claim:

1. In the recovery of fatty acids and neutral oils from vegetable oil soap stock, the process which comprises mixing the soap stock with at least one of the substantially water-insoluble solvents for the fatty components selected from the group consisting of aromatic hydrocarbons, halogenated hydrocarbons and petroleum naphtha hydrocarbons, adjusting the mixture to a pH of about 3.0 to 8.5 at a temperature below its boiling point while the mixture is being agitated whereby the soapstock impurities tend to concentrate in the aqueous phase,

6 separating the resulting fatty miscella from the aqueous phase at said temperature and removing the solvent from the fatty miscella.

2. In the recovery of fatty acids and neutral oil from vegetable oil soap stock, the process which comprises mixing the soap stock with water and at least one of the substantially water-insoluble solvents for the fatty components selected from the group consisting of aromatic hydrocarbons, halogenated hydrocarbons and petroleum naphtha hydrocarbons, adjusting the mixture by the addition of a mineral acid to a pH of about 3.0 to 8.5, at a temperature in the range of from about 65 F. to about F. and below its boiling point while the mixture is being agitated whereby the soap stock impurities tend to concentrate in the aqueous phase, separating the resulting fatty miscella from the aqueous phase at a temperature in said range and removing the solvent from the fatty miscella.

3. In the recovery of fatty acids, and neutral oil from vegetable oil soap stock the process which comprises mixing the soap stock with water and at least one of the substantially water-insoluble solvents for the fatty components selected from the group consisting of aromatic hydrocarbons, halogenated hydrocarbons and petroleum naphtha hydrocarbons, adjusting the mixture by the addition of a mineral acid to a pH in the range of from about 5.0 to 7.0 at a temperature in the range of from about 65 F. to about 135 F. and below the boiling point of the solvent while the mixture is being agitated whereby the soap stock impurities tend to concentrate in the aqueous phase, separating the resulting fatty miscella from the aqueous phase at a temperature in said temperature range and removing the solvent from the fatty miscella.

4. The process of claim 3 wherein the solvent is hexane.

5. In the recovery of fatty acids and neutral oil from vegetable oil soap stock, the process which comprises continuously flowing together and agitating soap stock, hexane, water and sulfuric acid, at a temperature in the range from about 65 to about 135 F., while regulating the iiow of sulfuric acid to control the pH of the resultant mixture to a value Within the range from about 3.0 to 8.5 whereby soap stock impurities tend to concentrate in the aqueous phase, continuously centrifuging the said mixture at a temperature in said temperature range to separate the fatty miscella from the aqueous phase, continuously distilling the separated aqueous phase to recover retained hexane, and continuously distilling the fatty miscella to remove the hexane therefrom.

6. In the recovery of fatty acids and neutral oil from cottonseed oil soap stock, the process which comprises mixing the soap stock with water and hexane, acidulating the mixture by the addition of sulfuric acid to a pH of from 5 to 5.5 at a temperature in the range of from about 65 F. to about 120 F. while the mixture is being agitated whereby the soap stock impurities tend to concentrate in the aqueous phase, separating the resulting fatty miscella from the aqueous phase at a temperature in said range and removing the hexane from the fatty miscella.

References Cited in the file of this patent UNITED STATES PATENTS 1,889,652 Gensecke c Nov. 29, 1932 2,054,096 Potts Sept. 15, 1936 2,171,202 Urbain et al Aug. 29, 1939 OTHER REFERENCES Oicial and Tentative Methods of Analysis of The A. O. A. C. Published by the Association of Ocial Agricultural Chemists, Washington 4, D. C., 6th edition, 1945 (pp. 525 and 526).

Bailey: Industrial Oil and Fat Products, 2nd edition, 1951, Interscience Publ., N. Y. C., pp. 646-649. 

1. IN THE RECOVERY OF FATTY ACIDS AND NEUTRAL OILS FROM VEGETABLE OIL SOAP STOCK WITH AT LEAST ONE OF THE SUBSTANMIXING THE SOAP STOCK WITH AT LEAST ONE OF THE SUBSTANTIALLY WATER-INSOLUBLE SOLVENTS FOR THE FATTY COMPONENTS SELECTED FROM THE GROUP CONSISTING OF AROMATIC HYDROCARBONS, HALOGENATED HYDROCARBONS AND PETROLEUM NAPHTHA HYDROCARBONS, ADJUSTING THE MIXTURE TO A PH OF ABOUT 3.0 TO 8.5 AT A TEMPERATURE BELOW ITS BOILING POINT WHILE THE MIXTURE IS BEING AGITATEDF WHEREBY THE SOAPSTOCK IMPURITIES TEND TO CONCENTRATE IN THE AQUEOUS PHASE, SEPARATING THE RESULTING FATTY MISCELLA FROM THE AQUEOUS PHASE AT SAID TEMPERATURE AND REMOVING THE SOLVENT FROM THE FATTY MISCELLA. 